I. Field of the Invention
This invention relates to an auxiliary axle assembly for work vehicles such as cement trucks. More particuarly, the present invention relates to an improved tag wheel axle assembly attached to the rear end of the vehicle which can be lowered to a ground engaging, truck supporting position or retracted to an elevated position so that the wheels straddle the sides of the truck frame above the ground where they will not engage obstacles in the truck's path.
II. Discussion of the Prior Art
Recently, there have been numerous efforts to develop improved tag axle assemblies which are attachable to a truck so that heavy trucks can meet weight restrictions.
Many governmental entities place road restrictions limiting the amount of weight any vehicle can carry while traversing roads and highways within their jurisidiction. Federal weight laws have a specific formula involving axles, the spacing of axles, and the length of the truck wheel base. Greater loads may, therefore, legally be transported by increasing the number of load bearing axles and wheel base to help support the vehicle.
Weight restrictions also have been expressed as a function of the distance between axles. By increasing the distance between axles, the weight is distributed over a greater portion of the road surface. Many restrictions of this type can be met by increasing the distance between the front and "back" axles of the truck by supply an auxiliary axle assembly which can serve as the "back" axle assembly.
Since tag axle assemblies of the general type under consideration can be an impediment when the vehicle reaches the construction site and must travel over rough, uneven and sometimes muddy or soft terrain, it has been the practice to design such tag axle assembly so that the wheels may be elevated once the vehicle is about to leave the public road surface. Thus, a very important element of any tag axle assembly design is to be able to easily and positively raise the assembly to a position where the assembly will have as much ground clearance as possible yet maintain the longest possible truck horizontal center of gravity.
Various entities, including applicant's assignee, have patented or are attempting to patent devices intended to help vehicles meet load limit restrictions. Applicant's assignee, for example, is the licensee of U.S. Pat. No. 4,492,389 and the owner of U.S. patent application Ser. No. 813,419, filed Dec. 26, 1985. As will be made clear from the subsequent discussion of the preferred embodiment, the apparatus of the present invention is somewhat similar to the apparatus described in U.S. patent application Ser. No. 813,419. However, the present invention is a great improvement over that apparatus because it is fool proof when extending the axle and wheel assembly. It is also easier to build and maintenance is less costly. With the present invention, the two auxiliary hydraulic cylinders present in the design described in U.S. patent application Ser. No. 813,419 have been eliminated. They have been replaced by solid steel bars secured to the frame by rubber or spring mounted anchors. This important modification eliminates certain problems associated with the hydraulic circuit of the old design by eliminating certain valves, hoses, and cylinders. The elimination of these parts solves problems inherent in the earlier design such as hydraulic leaking, bad seals, stones nicking the hydraulic piston rod and chrome deterioration of the piston rod.